Air is blowing out of defroster and floor but not main dash vents

usually a faulty blend door under the dash

The problem is either an actuator or the door associated with it. Sometimes the gear strips, especially when the system goes thru a recalibrate after power has been removed and reapplied. Below is a diagram of the locations of the actuators.

I think your problem is the head unit that selects where the air comes out ie. Face, floor, defrost, or hi-level face and floor. If that's not working then it will not let you switch location that you want the air to come out.

Often a sign of a blend door problem. The blend door or doors are in the heater a/c box behind the dash.

behind the center counsel between the floor and the heater housing is a part that is called the blend door actuator. these usually go bad and have to be replaced.

the switch where you turn it to blowing at your head is probably out. you will need to replace the switch control where your defrost, foot, head etc. what make, model, year is your vehicle?

Hope I was avle to help, glad you up and going.

common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.

You either have a bad control, or motor running the air direction door in the front HVAC unit, or a door that is stuck.

The front and rear units are totally separate.

The door directs where the air, cold or hot, should come out, whether it is panel vents, floor, defrost, or any combination of those.

This door and motor are located inside the heater box which usually requires a lot of the vehicle dash assembly to be taken apart to get to these parts.

i have the same problem.cold air comes out the dash then cuts off to the floor then cuts off to the defrost.the rear vent only blow out hot air.please help me to